Magnet core



Patented Jam 20, 1931 UNITED STATES PATENT. OFFICE PHILIP NORTON BOSEBY,OF LIVERPOOL, ENGLAND, ASSIGNOB TO ASSOCIATED TELE- PHONE AND TELEGRAPHCOMPANY, OF CHICAGO, ILLINOIS, A CORPORATION 01 DELAWARE MAGNET CORE NoDrawing. Applicationfiled April 27, 1029, Serial No. 858,760, and inGreat Britain June 13,1928.

as employed in telephone circuits. The ob- 5 ject of the invention isthe provision of a new and improved core material which is chea tomanufacture and can readily be forme to the desired shape and whichmoreover possesses in a high degree the properties most advantageous forcores in loading coils, viz. high specific gravity and high ohmicresistance.

It has been usual hitherto to construct cores for loading-coils bysubjecting a mixture of finely divided magnetic material with insulatingmaterial for magnetically separating the particles of magnetic material,to very high pressures so that the particles cohere and form a solidmass the specific gravity of which approximates tothat of pure-iron.

According to the present invention the insulating material comprises afilm of iron phosphate and the particles are preferably held together bya binder of synthetic resin varnish, for instance a phenol-aldehydecondensation product. p

In order that the invention ma be better understood one methodofcarrying it intoeffect will now be described. Use is preferably made ofcommercial iron powder which can be cheaply obtained, or use may be madeof a powdered iron alloy such, as ferro-silicon or nickel iron. Thepowdered iron is first annealed in air-tight pots at a temperature ofabout 600 C. and is then boiled in a solution of zinc phosphate. As aresult of this treatment an insulating film of metallic phosphate ofiron is formed on the surface of the iron particles. This film has igreat mechanical strength and very high electrical resistance and istherefore particularly suitable for loading-coil, dust cores, as itsmechanical strength enables it to withstand moulding at pressures of 20to 90 tons per square inch without losing its insulating properties andat the same time ensuring an initial permeablity approximating to thatof pure iron.

The magneto powder after being boiled in the solution of zinc phosphateis washed in water and dried. In order to bind the magnetic particlestogether they are next coated with one coat of synthetic resin varnishofsu table consistency,this varnish preferably being prepared from apowder composed of material known under the. registered trade name ofBakelite. The magnetic powder is then subjected to pressure of about 40tons per s uare inch in moulds heated to about 200 to form rings Therings may now be made up into loading coils for use on telephone linesand for this purpose a suitable number, for instance, from four toeight, are bound together with tape and are wound with two windings onoposite halves of the core followed by a further two windings on top ofthose previously wound. In use one mner winding is connected with theopposite outer winding, and the two coils thus produced form thewindings of the loading coil. The coil is then dried and embedded inresin.

It will be seen therefore that the arran ement according to theinvention permits t e cheap construction of satisfactory loading coilshaving properties which make them comparatively small in bulk and highlyefficient in use.

What I claim as new and desire to secure by Letters Patent is 1. Amagnet core composed oi finely divided iron particles, a coating of ironphosphate on sald particles, and insulating material separating saidphosphate coated particles.

2. A magnet core composed of finely divided particles of magneticmaterial, a coating of phosphate on said particles, and insulatingmaterial separating the phosphate coated particles.

3. The method ofmaking magnet cores, which consists in coveringparticles of magnetic material with a coating of phosphate of themagnetic material, then covering the coated particles with a bindingmaterial, and then forming a mass of the coated particles into a solidbody by pressure sufiicient to give it a specific gravity approximatingthat of. the magnetic material.

4. The method of making magnet cores, which consists in coveringparticles of pure iron with a coating of iron phosphate, thenproximating that of pure iron.

covering the coated iron particles with a. binding material, and thenformin a mass of the coated particles into a solid b y by pressuresuflicient to give it a specific gravity ap- 5. The method of makingmagnet cores, which consists in covering particles of pure iron with acoating of iron phosphate byboiling tlie ironcpartlcles in a solution ofzinc phosphate, then. covering said coated particles with a bindingmaterial, and then forming a mass of said coated particles into, a solidbody in a heated mold by pressure sufiicient to give it aspecificgravityapproximating' that of pure iron.

In testimony whereof I have signed my name at Liverpool, England, thisth day of 1 April, 1929.

PHILIP NORTON ROSEBY.

